The present invention generally relates to a microwave landing system and, more particularly, to azimuth guidance equipment and elevation guidance equipment which form a part of the ground installation of such a system and are constructed into a single assembly.
The ground installation of a microwave landing system includes azimuth guidance equipment and elevation guidance equipment which cooperate to provide angle information. It has been customary to construct the azimuth and elevation guides independently of each other and install each of them at a different location due to the process of development, the manner of operation and other various reasons particular thereto. However, it is not necessary that each of azimuth and elevation guidance information be transmitted from different locations, especially in a heliport. Both types of guidance equipment are essentially similar in construction to each other except for the arrangement of a radiating element array which constitutes a beam scanning antenna. Specifically, while the radiating element array of the azimuth guidance equipment is implemented as a waveguide slot array, that of the elevation guidance equipment is implemented as a printed board dipole array. The two different types of guidance equipment, therefore, can share a major part of the structural parts and elements with each other except for the radiating element array, and can be provided in a single assembly to constitute simple and inexpensive guidance equipment. Nevertheless, unitary azimuth and elevation guidance equipment has not been proposed in the past.
A prior art microwave landing system having a beam scanning antenna which is implemented as a phased array is provided with redundancy. However, a power amplifier, antenna switching unit and the like, which are included in both azimuth and elevation guidance equipment and constitute key elements of the system, are not provided with redundancy. When the system is constructed in a dual configuration, it is extremely difficult to provide the antenna switching unit with redundancy and therefore to enhance the reliability of operation.